Cool steps help fight global warming

By James Temple :
February 11, 2013
: Updated: February 11, 2013 7:39pm

Facilities project manager Andrew Mixer explains the energy efficient “cool roofing” on top of a library at a school in Richmond, Calif. “Cool roofs and pavement” are specifically made white roofs and pavement that reflect back more light and heat.

Photo By Michael Short/Special to the Chronicle

Board Regional Facilities Project Manager Andrew Mixer explains the energy efficient "cool roofing" on top of the library at King Elementary School in Richmond, CA Wednesday February 6th, 2013. "Cool Roofs and Pavement" are specifically made pavement and white roofs that reflect back more light and heat, using technology developed at Lawrence Berkeley Lab.

Photo By Michael Short/Special to the Chronicle

Energy efficient "cool roofing" is seen on the roof of the library at King Elementary School in Richmond, CA Wednesday February 6th, 2013. "Cool Roofs and Pavement" are specifically made pavement and white roofs that reflect back more light and heat, using technology developed at Lawrence Berkeley Lab.

Photo By Michael Short/Special to the Chronicle

Energy efficient "cool pavement" is seen on the playgound area of King Elementary School in Richmond, CA Wednesday February 6th, 2013. "Cool Roofs and Pavement" are specifically made pavement and white roofs that reflect back more light and heat, using technology developed at Lawrence Berkeley Lab.

When it comes to high-tech possibilities for counteracting climate change, the headlines tend to focus on the seemingly sci-fi stuff: brightening clouds, pumping particles into the stratosphere and launching giant mirrors into space.

But there are down-to-earth versions of the same basic concept, approaches as simple as painting roofs white or using light-colored pavement to cast away more heat from the Earth. A group at Lawrence Berkeley National Laboratories is exploring how big an impact this approach could have on global warming, as well as developing next-generation building materials that reflects more light.

Compared with more unconventional strategies, the advantages of white roofs and related concepts are that they're proven, cheap and relatively noncontroversial. The basic idea has been employed in sweltering parts of the world since the time of the pharaohs.

“It's so salable that people tend to smack their heads and say, 'Why didn't I think of that?'” said Arthur Rosenfeld, distinguished scientist emeritus in the environmental energy technologies division at Lawrence Berkeley, who is working with the lab's Heat Island Group. “There's a huge payoff.”

Indeed, if all “eligible” flat urban roofs worldwide were whitened, it could reflect away enough heat to offset the warming effect of 1.2 gigatonnes of carbon dioxide each year, according to research at the Heat Island Group. That's roughly one-thirtieth of annual global emissions.

It also could chip away at total greenhouse gas emissions; those cooler buildings wouldn't use as much energy for AC.

The total impact is far from the level theoretically promised by things such as cloud brightening or spraying sulfur particles into the stratosphere. Done on a large-enough scale, using machines under development to whiten clouds along coastlines could offset the warming effect from a doubling of carbon dioxide concentrations in the atmosphere, according to some studies.

But making roofs white can be done today. Making all flat roofs white would be equivalent to taking half the world's cars off the roads, in terms of the warming effect of CO
{-2}.

“Almost every potential step we take is a partial solution,” said Ronnen Levinson, the staff scientist who leads the Heat Island Group. “White roofs can by no means reverse global warming, but the cooling benefit is substantial, and it's something that's easily within reach.”

A 1995 Chicago heat wave killed at least 739 people; the highest-risk group lived on the top floors of buildings with black roofs. White roofs can stay up to 60 degrees cooler than traditional ones in summer sun.

That's a critical consideration as global warming increases the frequency and intensity of heat waves. The one that scorched much of Europe during the summer of 2003 reportedly killed more than 50,000 people.

That event was the turning point for Rosenfeld. As a member of the California Energy Commission at the time, he helped push through new building standards in 2005 requiring new or remodeled flat roofs on commercial buildings in the state to be white.

But flat roofs have been an easy target. It's a relatively simple sell, as public policy goes, because it lowers energy costs for building owners without requiring them to pay much, if anything, more. There is also no aesthetic downside because few see the top of flat roofs. The same, however, can't be said for the sloped roofs of most residential homes.

That's one reason the Heat Island Group, with the support of the Department of Energy, is developing roofing materials that look like conventional dark red or brown shingles, yet reflect back more heat.

The trick is using materials, such as titanium dioxide, that cast back more light in the near infrared spectrum. Our eyes can't perceive that light, but it makes up about half of the energy in the sunlight that reaches the Earth.

As of 2008, new or remodeled residential buildings in some of the hottest areas of the state also must have cool colored roofs, making California's rules the strictest in the nation, possibly the world.

The Berkeley Lab also is working with industry to develop cool versions of both asphalt concrete and cement concrete pavements. On a hot day, the cool pavement in its parking lot can be 30 degrees cooler than blacktop.

There are energy-efficiency grants for certain government structures such as schools that opt to use cool building materials. That's why King Elementary School in Richmond has a light-colored playground.

Outgoing Energy Secretary Steven Chu, previously the director at Lawrence Berkeley, pushed the cool roofs idea throughout his tenure in the Obama administration. He issued a memorandum in 2010 directing Department of Energy sites to install cool roofs whenever it was cost-effective at the time they were being replaced — and encouraged other agencies to do the same.

The American Society of Heating, Refrigeration and Air-Conditioning Engineers, which sets the national model codes that states and cities often adopt as mandatory rules, first put cool roof standards for flat-roofed buildings into effect for certain regions in 2007. An update due next year will widen that area to include Washington, Philadelphia and New York.